The invention relates to a firing device for a pyrotechnic vehicle-occupant protection device, in particular for motor vehicles. The firing device contains a terminal for an external supply line, an electronic unit with a voltage input and a control input that are connected to the terminal, a voltage output, and a firing output. A firing component is connected to the voltage output and to a firing switch that is connected to the firing output. The electronic unit generates a predetermined firing voltage at its voltage output when a supply voltage is applied to its voltage input, and when a firing signal is applied to its control input, generates a firing pulse at its firing output. The firing pulse actuates the firing switch with the result that the firing component fires.
Conventional firing devices for pyrotechnic vehicle-occupant protection devices, for example firing caps for gas generators of airbags or belt pretensioning devices are subjected to what is referred to as a xe2x80x9cBroustonxe2x80x9d test for quality assurance. In the test, a number of firing caps are extracted from a batch. A first voltage is then applied to a first firing cap. If the firing cap does not yet fire at the first voltage, the voltage is increased until firing occurs. After the firing of the firing cap, the voltage at which the first firing cap has fired is lowered again somewhat on a second firing cap. If the second firing cap does not fire, the voltage is slightly increased again until the firing cap fires, and so on. As a result, a firing distribution over firing voltages is obtained. The advantage of the initial Brouston test is that relatively reliable statistical data can be acquired with relatively few triggered and fired firing caps. The reason for the reliability of this data is that the voltage always fluctuates around the firing voltage.
Conventional firing caps have two terminals or terminal pins between which a firing bridge, for example a wire fuse is located. The firing voltage is applied to the terminals.
In modern firing devices that are actuated by a firing bus, an electronic unit, which generates a well defined and stabilized voltage and permits energy to be supplied to the firing cap only if a coded firing signal is detected at the terminal is connected between the cable-harness-end terminal, or the cable-harness end terminal pins, and the firing cap. This ensures a high degree of operational reliability. However, the intermediately connected electronic unit makes the Brouston test impossible. In such modern firing caps and firing devices there are no accessible connecting points between the electronic unit and the firing bridge.
It is accordingly an object of the invention to provide a firing device for a pyrotechnic vehicle-occupant protection device which overcomes the above-mentioned disadvantages of the prior art devices of this general type, in which there is a large degree of flexibility with respect to flexibility.
With the foregoing and other objects in view there is provided, in accordance with the invention, a firing device for a pyrotechnic vehicle-occupant protection device. The firing device contains a terminal for an external supply line and an electronic unit having a voltage input coupled to the terminal, a control input connected to the terminal, a voltage output, a firing output, and a test output. A firing switch is connected to the firing output. A firing component is connected to the voltage output and to the firing switch. A test switching device is connected between the terminal and the voltage input. The test switching device is connected to the test output of the electronic unit. A bypass line is connected between the test switching device and the voltage output. The test switching device disconnects a connection between the terminal and the voltage input and connects the terminal to the bypass line when a test signal is applied to the control input of the electronic unit. The electronic unit generates a predetermined firing voltage available at the voltage output when a supply voltage is applied to the voltage input, and when a firing signal is applied to the control input, the electronic unit generates a firing pulse available at the firing output. The firing pulse actuates the firing switch with a result that the firing component fires.
By using the switching device provided according to the invention it is possible to bypass the electronic unit and to test the firing device directly in a conventional way by applying an appropriate supply voltage or test voltage.
In accordance with an added feature of the invention, a charging resistor is connected in the bypass line for limiting a current flowing through the bypass line to a value at which the firing component does not fire.
In accordance with a further feature of the invention, the test switching device contains a MOSFET.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a firing device for a pyrotechnic vehicle-occupant protection device, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.